U.S. Pat. No. 6,024,453 is incorporated herein by reference. FIG. 1 (Prior Art) is a block diagram illustrating the invention taught in U.S. Pat. No. 6,024,453. It shows a color wheel 1 having filter segments 12 comprising wedges forming a disk which rotates about axis 10. Motor 2 acts on carrier 11, causing the color wheel to rotate and the filter segments to intercept light beam 6 from light source 5, as monitored by position sensor 3. As the color wheel rotates, the light passes through the filter segments in turn, projecting light of different colors along optical axis 60 in short bursts toward image generation device 7. The light reflects off of an image generation device 7, forming an image transmitted to projection lens 8, and then to a screen 9.
U.S. Pat. No. 6,024,453 describes the environment in which color wheels must operate. The wheel must rotate on the order of thousands of revolutions per minute, and must tolerate high temperatures (on the order of 100° C.) due to its proximity to light source 5. The position of filter segments 12, relative to each other and the axis or rotation, must be carefully maintained in order to balance the color wheel and achieve a long operational life of the device.
The method of attaching the filter segments to the carrier is as follows: the plain color filter segments are bonded on the periphery of the circular carrier via adhesive bonding applied where the glass segment overlaps the carrier. The bonding area is confined to a small ring zone near the center of rotation.
A balancing procedure is performed on the color wheel after fabrication, for example by selectively removing material from the carrier, forming recesses. The recesses may be selectively filled with a material such as adhesive or cement.
The color wheel fabrication procedure taught in this patent works well, but the fabrication process requires many steps. The glass segments are aligned and bonded onto the carrier with a photo-reactive adhesive, which then requires a secondary cure in a heat oven to finish the adhesive cure. The color ring is then attached to a motor with an adhesive such as epoxy, and this assembly is cured again in a heat oven.
Sometimes there are issues with curing the adhesive holding individual filter segments if the segments do not transmit the optimum wavelength for the photo-reactive adhesive. There is also an issue with stress induced by thermal expansion during the oven curing temperature of this adhesive.
A need remains in the art for an improved fabrication technique for color wheels.